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I had the opportunity to do P2P back in '90, to Russia, but did not because of the expense. This is one of the few things I regret in my life.
I really wish I had done it. Especially with all of the "history" that happened during that time and soon after.
I have a a good friend who did take the P2P trip to Russia a year later and she told me it was the most eye opening experience she had ever had.
I agree with what IDontLikeYouInThatWa said, although since your son is going to Oz, imo it would be like a trip to Canada (with just a much longer flight).
Even if your son was not the most mature, I would still encourage you to give him the opportunity to go.
Sure he may go to Australia someday but probably never "on his own" (as a kid) and in the scenario of integrating himself as much into the culture with a host family.
A trip like this, imo, would do wonders in helping someone grow up / mature.